Japanese Laid-Open Application Nos. H9-230248 and H3-87804 each disclose a probe in which is mounted a small-sized, confocal point optical system. The confocal point optical systems disclosed by these references are of the side-view-type, in which the view field is orthogonal to the longitudinal direction (i.e., the insertion direction) of the probe.
On the other hand, FIG. 7 shows an endoscope having a direct-view-type optical system in which the insertion direction of the probe and the direction of the visual field correspond. When a side-view-type confocal point optical system probe is used through a channel, such as the forceps channel, of an endoscope, the observation range of the confocal point optical system probe is difficult to determine. However, in the case of an endoscope using a direct-view-type confocal point optical system, it is easier to specify the observation range of the endoscope image. An improvement in operability is thus achieved when using a direct-view-type confocal point optical system in an endoscope as compared to using a side-view-type confocal point optical system.
Thus, there is a need for a small-sized, direct-view-type confocal point optical system which can be used in conjunction with an endoscope. Because the reflection factor of objects normally viewed with an endoscope (e.g., tissue of a living organism) is low, the signal component which is reflected and then received to be viewed or photographed is very small. Therefore, it is essential to suppress, as much as possible, unwanted light (i.e. the noise component), such as light reflected by lens element surfaces and other reflecting surfaces of the optical system. This is especially the case in a direct-view-type optical system, wherein the optical components generally tend to be arranged along a straight line. For this reason, it is important to reduce the noise component of light in the image of the object being observed.
This invention relates to a small-sized confocal point optical system, especially a small-sized confocal point optical system which is used through a channel of an endoscope. The object of the invention is to reduce the noise component of light in an image of an object being observed using a direct-view-type confocal point optical system in conjunction with an endoscope.